Vulcanizing synthetic rubber with dixanthic sulfides



Patented Nov. Iii, 1948 VULCANIZING SYNTHETIC RUBBER WITH DIXANTHIC SULFIDES David J. Beaver, St. Albans, W. Va., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation 01' Delaware No Drawing. "Application September 13, 1943, Serial No. 502,191

12 Claims. 1

The present invention relates to a method of vulcanizing synthetic rubber and to the vulcanized rubber products obtained.

It is an object of this invention to provide an improved method of vulcanizing a synthetic rubher. A further object is to vulcanize a sulfur vulcanizable synthetic rubber in the, absence of free sulfur. Still another object is to provide synthetic rubber vulcanizates of improved properties. Other objects will be apparent from the detailed description following.

In accordance with the present invention it has been discovered that xanthic sulfides are valuable vulcanizing agents for synthetic rubber. The xanthic sulfides possess the structure where R is an organic radicle having an alkyl carbon atom linked to the oxygen and n is an integer greater than one. Typical examples of it include allyl, methyl, ethyl, propyl, butyl, amyl, hexyl, octyl, decyl, lauryl, cyclohexyl, benzyl, methoxy ethyl, ethoxy ethyl and the like but the invention is not limited thereto. The xanthic sulfides are prepared from the corresponding xanthates in known manner. Oxidising a solution of an alkali metal xanthate with hydrogen peroxide, chlorine, hypochlorite, persulfate or other oxidizing agent produces a xanthic disulfide. Higher sulfides are prepared by reacting the xanthate with a sulfur halide. Also useful in erator are added. While the xanthic sulfides contain sulfur in the molecule, their vulcanizing action is different from that of elemental sulfur since the vulcanizates possess different properties. The vulcanlzates prepared in the presence of xanthic sulfides much more closely resemble natural rubber.

Some thermoplastic products prepared synthetically especially the emulsion copolymers of butadiene-l,3 and vinyl compounds containing the single pclymerizable group this invention are polymeric xanthic sulfides in which case the xanthic sulfide nucleus is repeated a number of times in a single compound. For example, diethylene glycol was reacted with carbon disulfide in alkaline solution to produce the xanthate and from the xanthate a polymeric xanthic sulfide was produced by oxidizing with hydrogen peroxide or other oxidizing agent. The product was a hard grindable resin which nossessed strong vulcanizing action in synthetic rubber as for example Buna S.

A sulfur vulcanizable synthetic rubber will vulcanize in the presence of a xanthic sulfide without the presence of auxiliary agents. The time required for vulcanization can be greatly shortened by the application of heat and for best results a small amount of an inorganic activator,

preferably zinc oxide, and a thiazole type accelresemble natural rubber in most of the properties commonly associated with the latter. For example the synthetic productsare sulfur vulcanizable and exhibit the properties of elasticity and recovery. However, one of the most serious shortcomings of the synthetic rubbers is greater brittleness and lower elongation than natural rubber. While the synthetics resist aging as well or better than natural rubber, their lower initial properties result in vulcanizates which, especially after exposure to the air in service, are unsatisfactory for many of the uses required of arubber stock. On the other hand the xanthic sulfide vulcanizates possess elastic properties which resemble those of natural rubber much more closely and retain them to a remarkable degree after exposure to air or oxygen. While the amount of xanthic sulfide may vary widely and cures have been obtained with as little as 1% or 2% on the rubber of the xanthic sulfide, optimum results are obtained with such quantity as contains 2% sulfur based on the rubber.

The following are specific embodiments of the invention illustrating the invention and arenot to be taken as limitative thereof.

A base stock was compounded comprising Parts by weight Buna B 100 Carbon black Zinc oxide N-c y c 1 o h e x y l z-benzothiazole sulfenamide 1.2

Emulsion copolymer of butadiene-1,3 and styrene.

From the base stock a control stock was prepared by adding 1.75 parts by weight of sulfur Etheyl xanthic tetrasulfide 5 2,458,689 3 4 and other stocks were prepared by adding 6.0 As further embodiments of the invention synparts by weight of a xanthic disuiflde in place of thetic rubber stocks were compounded comprising the sulfur.

Stock Stock Xantbio Sulfide 5 l h 1 thi disulflde yco exy mu Octyl xsnthlc disullide. :353? :25:13 Hexyl xanthic dlsuliide. 100 100 Amyl xanthic dlsulflde. 55 55 Butyl xanthic disuliide. 5 g r py g}g g smile Acid" 2 2 y m c h 2- is m1 1 Methylmthlc disulfldeg 2 Methoxy ethyl xanthic disulflde 6 The stocks so compounded were cured by heating for 90 minutes in a press at the temperature of 40 pounds of steam pressure per square inch. The modulus and tensile properties of the vulcanized products were determined both before and after aging in an oven for 24 hours at 100 C.

The stocks so compounded were cured by heating in a press for 60 minutes at the temperature of 40 pounds of steam per square inch. The modulus and tensile properties of the cured rubber products were determined both before and after aging in an oven at 100 C. for 24 hours.

Table X Table In Modulus of Modulus of Elasticltyin Tensile at Ult. E] 1 1 Stock lbs/inPat Break in Elong, 25 BM a 51,? "g gg i g Elongation -l Per Gen Elongation lbs/in. Per Cent of 300% o! 300% 2 250 2,440 385 11210 2,480 195 1,34 1% 2,700 510 315 2, 630 375 2,250 510 ziig The above data shows that a difierent type of 1.730 2% cure is obtained than with ordinary sulfur vul- 590 canization since similar tensiles but much higher 2, 250 60g elonsations are obtained. g;% 25 Further stocks were compounded comprising 2.460 515 2, 170 400 1,310 510 Stock M N o The above data show the superior physical properties-of vulcanizates prepared in the presence of 52,311 :32; 31! 1: :58 511 a, xanthic sulfide in contrast to ordinary Sulfur BqnaS 100 100 IgO vulcanization. gg g g 40 g g 110 m e As a, further'speclfic embodiment of the inven- 113E1 xgg2icdtifi1iflfl(:e 37 3.7 3 77 BT08!) 1120 820 9. tion a rubber stock was compounded comprising 1,3? a t ggag 1 fi d {In M5 1m 0k m eafi nui 0. 95 7 parts by welsht 5e 7 Bllna, S

t e stocks so com unded were vulcanized-b Carbon blackheating in a press for minutes at 142 C. The modulus and tensile properties of the cured rubber The stock so compounded was cured by heating 55 products were determined before and after aging in a press for 180 minutes at the temperature of m an Oven 24 hours at 40 pounds of steam pressure per square inch. The Table IV modulus and tensile properties of the cured product are given below.

' Modul r El Table II 80 ucu mlbs/ig i at Elongations Tensile at I Ult. Stock oi- Break E1ong.,

Modulus of Elasticity lbs/in. Per Cent Emma Tensile at Ult. 200% 30 Stock Break in Elong,

lbs/in. Per Cent 340 650 2 m0 600 200% 625 1, 210 21430 500 I :38 v 1 $8 1% The above data show that the xanthic sulfides are Very active 110911121118 agents even in the The above data show the excellent physical propabsence of auxiliary agents such as accelerators w possessed by vulcanizates prepared in the and activators. In fact two days standing of the .presence of a xanthic sulfide. While the quantity unvulcanized stock at room temperature was used in the above stocks is about the optimum for found to effect a cure. is the best physical properties, good cures have been obtained with as low as 1.9 parts by weight of ethyl xanthic disillfide and as much as 11.3 parts by weight.

Again, this invention is not limited to the specific compositions set forth to illustrate the invention. Other ratios of the compounding ingredients than those mentioned in the examples as well as other well known fillers, pigments and the like may be employed in the production of various types of synthetic rubber compounds as will be apparent to those skilled in the art to which this invention pertains. Other accelerators than those mentioned can be used. An extended study has revealed that a wide variety of accelerators are satisfactory for use in, conjunction with a xanthic sulfide for vulcanizing synthetic rubber. For example, rubber stocks of excellent physical properties were obtained by vulcanizing Buna S with ethyl xanthic disulfide in the presence of any of the following accelerators: benzoyl 2- benzothiazyl sulfide, bis(6-phenyl benzothiazyl) disulfide, bis(6-nitro benzothiazyl) disulflde, the cyclohexylamine salt of 2-mercaptobenzothiazole, bis(4-phenyl.benzothiazyl) disulfide and a mixture of his 4, 5-dimethyl thiazyl disulfide and bis-d-ethyl thiazyl ,disulfide. While the mercaptothiazole type accelerators, particularly z-mercaptobenzothiazole and itsderivatives are preferred, good results have been obtained with -o-'os.-c-oi i where am an integer at least two but less than five and heating the mixture.

2. The process of vulcanizing a synthetic sulfur the nucleus vulcanizable rubber like material comprising the emulsion copolymer of butadiene-1,3 and styrene which comprises adding to the rubber in the absence of elemental sulfur a dixanthic disulflde and heating the mixture.

3. The process of 'vulcanizing a synthetic sul- 55 fur vulcanizable rubber like material comprising the emulsion copolymer of butadiene-1,3 and styrene which comprises adding to the rubber in theabsence of elemental sulfura di-(alkyi zanthic) disuifldeand a thiazole accelerator and no heating the mixture.

4. The process of vulcanizing a synthetic sulfur vulcanizable rubberlike material comprisin the emulsion copolymer of butadiene-1,3 and styrene which comprises adding to the rubber in the absence of elemental sulfur a di- ('alkyl xanthic) disulflde in such amount as contains about 2 parts by weight sulfur based on the rubber and an arylene thiazole accelerator and heating the mixture.

5. The process of vulcanizing a synthetic sulfur vulcanizable rubber like material comprising the emulsion copolymer of butadiene-1,3 and styrene which comprises adding to the rubber in the absence of elemental sulfur di-(ethyl xanthic) disulflde in such amount as contains about 2 parts by weight sulfur based on the rubber and an arylene thiazole accelerator and heating the mixture.

6, The process of vulcanizing a synthetic sulfur vulcanizable rubber like material comprising the emulsion copolymer of butadiene-1,3 and styrene which comprises adding to the rubber in the absence of elemental sulfur di-(butyl xanthic) disulfide in such amount as contains about 2 parts by weight sulfur based on the rubber and an arylene thiazole accelerator and heating the mixture.

7. The vulcanized synthetic rubber product obtained by the process of claim 2.

8. The vulcanized synthetic rubber product obtained by the process of claim 3.

9. The vulcanized synthetic rubber product obtained by the process of claim 4.

10. The vulcanized synthetic rubber product obtained by the process of claim 5.

11. The vulcanized synthetic rubber product obtained by the process of claim 6.

12. A composition vulcanizable upon heating which comprises a synthetic sulfur. vulcanizable rubber like copolymer of butadiene-1,3 and styrene having incorporated therein, instead of elemental sulfur, a di-xanthic sulfide containing the where n is an integer at least two but less than five.

DAVID J. BEAVER.

REFERENCES CITED The following referencesare of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,634,924 Whitby July 5, 1927 2,234,204 Starkweather et al. Mar. 11, 1941 2,248,103

Meisenburg et al. July 8, 1941 

